Under the cab below the clutch peddle is an adjustment for the clutch (two threaded rods go into a long adjustment nut)
What your describing though sounds like slipping in the torque amplifier, fistly check to see if you have enough oil in the ass end (80/90 oil) anything lighter and it will also slip, secondly if it is the TA slipping it may need adjusting as follows:
1.Drain transmission oil
2.Unbolt brake cylinder cover(Square with 4 bolts and a round lump in the middle of it on LH side of gearbox near the bottom)
3.Remove spring and replace cover.
4.Tighten large adjusting screw with (22mm??)locknut above cylinder cover until it becomes tight and then slacken off 1 1/3-1 1/2 turns.
5.Tighten brake band.There are 3 screws with (17mm??)locknuts.One on each side of the transmission and one on top under the panel in the floor.Tighten each screw until it just becomes tight and slacken off by 1/3 turn and tighten locknuts.
6.Remove bolt on cover on RH side and you can see the torque mutiplier drum.Check that the drum still turns freely.
7.Reinstall spring in the brake cylinder.
8.Replace cover plate on RH side.
9.Replace transmission oil.
Thats the condensed version from the
manual .They say you can park the tractor facing uphill and save having to drain the transmission but if you leave the oil to settle and put the good stuff back and top up the rest with fresh oil you will have done two jobs at once!
On a JD they made all this self adjusting
If it is still slipping the band itself may be to far worn and need replacing, or you could be lucky and it's just the clutch plate
